1. Field of the Invention
Apparatuses and methods consistent with the present invention relate generally to wireless communication technology, and more particularly to ensuring efficient and stable data transmission when large-capacity asynchronous data is transmitted wirelessly.
2. Description of the Prior Art
As generally known in the art, networks tend to be used on a wireless basis, and the request for large-capacity multimedia data transmission is ever-increasing. As a result, it is necessary to provide an efficient transmission method in wireless network environments. Considering the characteristics of wireless networks, in which different devices share and use given wireless resources, increased contention may cause collision during communication, which results in the loss of a large amount of data. This means that valuable wireless resources may be wasted. In order to reduce such collision or loss and guarantee stable data transmission/reception, it is customary to use a contention-based DCF (Distributed Coordination Function) or contention free PCF (Point Coordination Function) in wireless LAN (Local Area Network) environments and to use a type of time division, particularly channel time allocation, in wireless PAN (Personal Area Network) environments.
Although these methods may lessen collision and ensure stable communication to some degree when applied to wireless networks, the possibility that collision between transmitted data will occur is still higher than in the case of wired networks. This is because wireless network environments essentially have a large number of factors adversely affecting stable communication, such as multi-path properties, fading, and interference. In addition, the more wireless networks that participate, the higher the possibility of problems (e.g. collision, loss).
Such collisions require retransmission, which fatally affects the throughput of wireless networks. Particularly, in the case of AV (Audio/Video) data requiring a higher level of QoS (Quality of Service), it is a crucial issue to reduce the number of retransmissions and secure more bandwidth.
Considering the current trend of requesting wireless transmission of high-quality video, such as DVD (Digital Video Disk) images or HDTV (High Definition Television) between various home devices, there is now a need to provide technological standards for seamlessly transmitting/receiving high-quality video.
A task group under IEEE 802.15.3c is preparing a technological standard for transmitting large-capacity data in wireless home networks. This standard, commonly referred to as mmWave (Millimeter Wave), uses radio waves having millimeter-grade physical wavelengths (i.e. radio waves having a frequency of 30-300 GHz) for large-capacity data transmission. Such a frequency domain has conventionally been used as an unlicensed band in limited applications (e.g., for communication business providers, for the purpose of radio-wave astronomy or vehicle collision prevention, etc.).
FIG. 1 shows a comparison between a frequency band based on an IEEE 802.11 series standard and one based on mmWave. It is clear from the drawing that IEEE 802.11b or IEEE 802.11g uses a band of 2.4 GHz and a channel bandwidth of about 20 MHz. In addition, IEEE 802.11a or IEEE 802.11n uses a band of 5 GHz and a channel bandwidth of about 20 MHz. In contrast, mmWave uses a band of 60 GHz and a channel bandwidth of about 0.5-2.5 GHz. This means that mmWave has a much larger frequency band and a smaller channel bandwidth compared with conventional IEEE 802.11 series standards.
As such, use of a high-frequency signal having a millimeter-grade wavelength (i.e. millimeter wave) guarantees that the transmission rate reaches the level of tens of Gbps and that the antenna has a size less than 1.5 mm. This means that a single chip incorporating an antenna can be implemented. In addition, a very high attenuation ratio in the air reduces interference between devices.
However, considering that the high attenuation ratio shortens the reach and that signals tend to propagate straightforward, proper communication can hardly be ensured in non-line-of-sight environments. Therefore, under mmWave it is proposed that the former problem be solved by using an array antenna having high gain and the latter problem by a beam steering scheme.
In addition to technology for transmitting compressed data by using a band of tens of Gbps based on conventional IEEE 802.11 series in home or office environments, it has recently been proposed to transmit uncompressed data by using a millimeter wave in a high-frequency band of tens of Gbps. As used herein, uncompressed data refers to data which is not compressed in terms of loss encoding. This means that lossless encoding may be employed as long as complete restoration is guaranteed.
Particularly, uncompressed AV data is large-capacity data which has not been compressed, and cannot be transmitted but in a high-frequency band of tens of Gbps. Compared with compressed data, uncompressed AV data hardly affects the display even if there is a packet loss. This means that ARQ (Automatic Repeat Request) or retry is unnecessary. Therefore, it is requested to provide a method for ensuring efficient medium access so as to properly transmit uncompressed data in a high-frequency band (tens of Gbps) having the above-mentioned characteristics.